This invention relates to the field of medical devices, and more particularly to a balloon catheter having a lobed balloon.
In percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire, positioned within an inner lumen of an dilatation catheter, is first advanced out of the distal end of the guiding catheter into the patient""s coronary artery until the distal end of the guidewire crosses a lesion to be dilated. Then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient""s coronary anatomy, over the previously introduced guidewire, until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with liquid one or more times to a predetermined size at relatively high pressures (e.g. greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall and the wall expanded to open up the passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. Substantial, uncontrolled expansion of the balloon against the vessel wall can cause trauma to the vessel wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom.
In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter, and the stent is left in place within the artery at the site of the dilated lesion.
In the design of catheter balloons, balloon characteristics such as strength, flexibility and compliance must be tailored to provide optimal performance for a particular application. Angioplasty balloons preferably have high strength for inflation at relatively high pressure, and high flexibility and softness for improved ability to track the tortuous anatomy and cross lesions. The balloon compliance is chosen so that the balloon will have a desired amount of expansion during inflation. Compliant balloons, for example balloons made from materials such as polyethylene, exhibit substantial stretching upon the application of tensile force. Noncompliant balloons, for example balloons made from materials such as PET, exhibit relatively little stretching during inflation, and therefore provide controlled radial growth in response to an increase in inflation pressure within the working pressure range.
In order to decrease the cross sectional profile of the balloon catheter to thereby facilitate advancement of the catheter within the patient""s vasculature and across a stenosed region, balloons may be folded into a low profile configuration having balloon wings wrapped around the balloon prior to insertion into the patient. However, one difficulty has been after the balloon is inflated in the patient and subsequently deflated, the balloon tends to form a large flat wing or a bunched up irregular shape. The resulting relatively large profile of the deflated balloon tends to complicate repositioning or removal of the balloon in the vasculature.
It would be a significant advance to provide a catheter balloon with improved refold after inflation of the balloon.
The invention is directed to a balloon catheter including an elongated shaft, and a balloon on a distal shaft section having at least a section which has an uninflated configuration or partially inflated with at least two lobes, and which has an inflated configuration with a cylindrical surface. In a presently preferred embodiment, the balloon has a lobed inner surface and a lobed outer surface. In one embodiment, the balloon has a uniform wall thickness around a circumference of the lobed balloon section. However, in alternative embodiments the balloon wall thickness may be nonuniform around the balloon circumference. Each lobe forms a wing when the balloon is deflated. The deflated wings provide a deflated balloon with a relatively low profile, which facilitates advancement of the catheter balloon across a stenosis and the repositioning or removal of the balloon catheter within the patient""s vasculature.
The lobed balloon section preferably extends at least the length of the working length of the balloon, and in one embodiment, the lobed section includes at least a portion of the tapers at one or both ends of the working length of the balloon. Additionally, in one embodiment, the lobed section includes a stepped, smaller diameter section proximal and/or distal to the working length. The lobes are disposed around the circumference of the balloon. The lobes may have a variety of suitable shapes, such that the lobes preferentially collapse during deflation of the balloon to each form a deflated wing. In a presently preferred embodiment, each lobe has a curved or cylindrical shape. In an alternative embodiment, the lobes have an angled configuration such as a triangular shape.
In a presently preferred embodiment, the balloon has about 2 to about 10 lobes, and preferably at least three lobes. The number of lobes depends on the inflated diameter of the balloon within the working pressure range of the balloon. Specifically, larger diameter balloons will preferably have a greater number of lobes than a smaller diameter balloon, to thereby form a greater number of deflated wings. By increasing the number of deflated wings, the overall size of each wing is reduced to a point where the deflated balloon profile is sufficiently low. In a presently preferred embodiment, a balloon having a 3.0 mm inflated working outer diameter has three lobes, and a balloon having a 4.0 to 6.0 mm inflated working outer diameter has four to six lobes. However, the number of lobes will depend on the desired performance of the balloon, so that larger diameter balloon having an inflated working outer diameter of greater than 3.0 mm may have as little as 2 or 3 lobes.
The balloon inflates into a cylindrical shape, which in a presently preferred embodiment forms when any substantial inflation pressure above atmospheric pressure is applied inside the balloon. Thus, the lobes are not identifiable when the balloon is inflated at elevated pressure, but are identifiable on the balloon when the balloon is at or near atmospheric pressure. The balloon is inflated to the cylindrical inflated configuration to perform a procedure such as dilatating a lesion, implanting a stent, or post-dilatation touch-up in the patient""s blood vessel.
In a presently preferred embodiment, the balloon is formed in a mold having the lobed shape. Thus, a polymeric tube is placed in the mold and inflated therein, generally at elevated temperatures, to form the balloon having the lobed shape. The polymeric tube may be configured to provide a balloon with substantially uniform or nonuniform wall thickness. As a result of being expanded in the mold, both the outer surface of the balloon and the inner surface of the balloon develop the lobed shape. Consequently, the balloon consistently deflates with wings formed by each lobe during removal of the inflation fluid from the balloon, and without the need to hold the interior of the balloon under vacuum after removal of the inflation fluid therefrom to force the wings to form. Additionally, the rupture and compliance characteristics of the balloon can be made uniform around the circumference of the balloon due to the uniform nature of the balloon wall.
The balloon of the invention provides excellent ability to cross stenosed or otherwise narrow regions of the patient""s vasculature, and deflates to a low profile configuration due to the uninflated configuration having lobes which form deflated wings. Additionally, the balloon inflates easily to a desired cylindrical cross section. These and other advantages of the invention will become more apparent from the following detailed description of the invention and the accompanying exemplary drawings.